34 MANUAL OF BACTERIOLOGY. 



it is intended it should touch. With such a platinum wire, 

 which has been properly sterilized, one can easily remove 

 portions from a culture of bacteria, or from a fluid in 

 which bacteria are supposed to be present. The glass rod 

 in which the platinum wire is fixed should be held between 

 the thumb and forefinger of the right hand like a pen. (For 

 the manner of holding test-tubes, see page 84.) 



The Hanging-drop. Living bacteria may be studied 

 with the microscope while suspended in some fluid sub- 

 stance. The needle having been heated to a red heat in 

 the flame and having been allowed to cool, a small portion 

 of the culture or other material may be removed with it 

 and deposited in the center of an ordinary cover-glass. 

 The needle should again be sterilized in the flame. When 



FIG. 6. 



Diagram of the hanging-drop. 



cultures on solid media arc to be examined, a small particle 

 may be mixed with a drop of sterilized water or bouillon. 

 The cover-glass should have been carefully cleaned and 

 sterilized over the flame. The cover-glass with the small 

 drop of fluid material held in sterilized forceps is now to be 

 inverted over a sterilized glass slide, which has a concavity 

 ground in the middle of it. Around the concavity, the slide 

 should be smeared with vaseline. In this manner a small 

 air-tight chamber is made. This slide and cover-glass may 

 be put upon the stage of the microscope. A good dry lens, 

 if of sufficiently high power, is more convenient for ex- 

 amining the hanging-drop than an oil-immersion. If the 

 latter be used, having placed a drop of cedar-oil on the 

 center of the cover-glass, and a good light having been 

 secured, the oil-immersion objective should be brought 



